import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @param o1 int整型 
     * @param o2 int整型 
     * @return int整型
     */
    public int lowestCommonAncestor (TreeNode root, int o1, int o2) {
        // write code here
        if(root == null) {
            return -1;
        }
        int left = lowestCommonAncestor(root.left,o1,o2);
        if(left >= 0) {
            return left;
        }
        int right = lowestCommonAncestor(root.right,o1,o2);
        if(right >= 0 ) {
            return right;
        }
        if(left == -1 && right == -1) {
            if(root.val == o1 || root.val == o2) {
                return -2;
            } else {
                return -1;
            }
        } else if(left == -2 && right == -2) {
            return root.val;
        } else if((root.val == o1 || root.val == o2) && (left == -2 || right == -2)) {
            return root.val;
        } else if((left + right) == -3){
            return -2;
        } else {
            return -1;
        }
    }
}